The present invention is related to optical devices; more particularly, the invention relates to mechanical optical switches.
The optical switch is a device for directing optical signals along selected fibers of an optical network, in which light signals are transmitted along optical fibers to transfer information from one location to another. Desirable optical switch properties include: high speed switching, low optical insertion loss, good repeatability, long operation lifetime, small size, and low cost. The optical switch is a key component in today""s optical networks, analogous to the electrical switches in electrical networks. However, it has not been widely adopted because of lack of reliability and high cost associated with fabrication difficulty.
Mechanical fiber optic switches using movable light guiding elements for alternating optical beam paths to effectuate switching are the dominant optical switching component used in current telecommunication systems. This is because, in comparison with other means, mechanical optical switches are simpler in construction and impose smaller distortions on the optical signals. For example, current non-mechanical switching technologies are based on changes of either optical phase or polarization. Consequently they have intrinsic drawbacks of polarization and wavelength dependence and induce signal distortions that become problematic as the channel count and transmission speed increase in next generation network systems.
In an optical switch, a light signal must be accurately entered into an optical fiber, or much of the signal strength will be lost. The alignment requirements of modern single mode optical fibers are particularly stringent, as their core diameters are typically as small as 2 to 10 micrometers and their acceptance angle is fairly narrow. For optical switches, alignment and maintenance of precision optical paths have been the main technical difficulty, since a slight misalignment can cause large insertion losses. Therefore, the cost and reliability of mechanical optical switches are primarily determined by the fiber alignment/package design.
Prior mechanical optical switch designs incorporate fiber collimator lenses, such as Graded Refractive Index (GRIN) lenses, to increase the alignment tolerance to some extent. The collimator tenses enlarge the optical beams at least ten to one-hundred times larger so that insertion losses will not significantly increase when there is a few micrometers of misalignment between the light path from the input fiber to the output fiber. However, the use of individual collimator lenses disadvantageously increases the separation between adjacent fibers, resulting in the need for large beam displacement for light path switching. Consequently, mechanical optical switches using individual fiber collimators have suffered from slow switching speeds and poor stability. An example of such an optical system is disclosed in U.S. Pat. No. 5,642,446.
A more recent version as described by Li et al. in U.S. Pat. No. 6,215,919 represents so me improvement by using a dual fiber collimator in which two fibers are placed next to each other and share a single imaging lens, substantially reducing the beam separation and overall device size. A disadvantage of Li""s switch is that the beam propagations are not parallel, and are instead at an angle. Consequently the switch demands precise fabrication of a moveable prism with matching wedges that not only precisely displaces the beam path but also must satisfy tight angular deflection relations. As a result, this type of switch requires high precision for maintaining accurate alignment of each optical path, in which the angular and the spatial positions are interrelated. This type of switch is therefore often very difficult and costly to make and its operation is less stable.
For the above reasons, current mechanical optical switches are expensive to produce and prone to fail with a short operation lifetime.
Accordingly, it is an object of the invention to provide a type of mechanical optical switch that utilizes compact optical elements and is insensitive to both angular variations and position shifts of the moveable light-guiding element. The present inventive mechanical optical switches therefore provide critical advantages of switching a light beam between an input fiber and output fibers with unprecedented stability and longevity against environmental perturbations and wear-out.
It is a further object of the invention to provide a type of mechanical optical switch which requires significantly reduced alignment steps having large assembly tolerances that is suitable for low-cost volume production,
The above objects and advantages, as well as numerous improvements attained by the apparatus and method of the invention are pointed out below.
It is an object of the present invention to provide a compact and economical optical switch that can be efficiently coupled to plural optical fibers such that these light couplings are less sensitive to misalignment of the movable light guiding switching element. The invention provides optical switches having at least three ports for optical fibers. The inventive switches use at least one single lens for coupling two fibers for compactness. The invention includes a light-bending device, situated to compensate for the angle between the two light beams that share the same lens, by advantageously rendering them parallel. The inventive switches rely on spatially shifting light propagation of parallel beams, desirably increasing alignment tolerance and thus stability and longevity.